A Man With Bilateral Arm Weakness After Lumbar Surgery

A 42-year-old man was referred with a 3-week history of weakness in both arms after he underwent a complicated lumbar laminectomy for severe chronic, posttraumatic low back pain and a disk rupture. The surgery lasted longer than normal. When he woke up from surgery he could not flex his arms but had no other neurologic problems. Past medical history was unremarkable except for hypertension. There was a strong family history of diabetes. The patient did not smoke or drink.

Examination revealed normal mentation and cranial nerves. Strength was normal and symmetric except for significant weakness and atrophy ( Fig. 10-1 ) in both biceps with normal brachioradialis muscles, and he used his brachioradialis to flex the arms. Other upper extremity muscles appeared grossly normal. Reflexes were 2+ in the triceps, knees, and ankles and left brachioradialis; both biceps and right brachioradialis reflexes were absent. There was decreased pain sensation in the lateral aspect of the forearm. The rest of the examination was normal except for the lumbar laminectomy scar.

MRI of the neck and the brachial plexus with and without gadolinium done prior to referral was normal.

An EMG Test was Performed

Motor Nerve Studies

Nerve and Site	Latency (ms)	Amplitude (mV)	Conduction Velocity (m/s)
Median Nerve R.	Normal ≤ 4.2	Normal ≥ 6	Normal ≥ 50
Wrist	4.0	13	–
Elbow	9.4	13	51

Ulnar Nerve R.	Normal ≤ 3.6	Normal ≥ 8	Normal ≥ 50
Wrist	3.0	11	–
Below elbow	8.5	11	48
Above elbow	10.8	11	52
Axilla	13.7	11	62
Erb’s point	NR	NR	NR

Median Nerve L.	Normal ≤ 4.2	Normal ≥ 6	Normal ≥ 50
Wrist	4.4	10	–
Elbow	10.4	9	48

Nerve and Site	Latency (ms)	Amplitude (mV)	Conduction Velocity (m/s)
Ulnar Nerve L.	Normal ≤ 3.6	Normal ≥ 8	Normal ≥ 50
Wrist	2.6	12	–
Below elbow	7.9	12	50
Above elbow	9.5	12	68
Axilla	12.3	12	54
Erb’s point	NR	NR	NR

Peroneal Nerve R.	Normal ≤ 5.7	Normal ≥ 3	Normal ≥ 40
Ankle	3.5	6	–
Fibular head	12.7	5	36
Knee	15.6	5	31
Musculocutaneous nerve R.		Normal ≥ 8
	8.6 ^a	2	–
Musculocutaneous nerve L.		Normal ≥ 8
	4.5 ^a	3	–

a Side-by-side comparison: more than 2 ms difference is significant.

F-Wave Studies

Nerve	Latency (ms)	Normal Latency ≤ (ms)
Median nerve R.	33.1	30
Ulnar nerve R.	34.2	30
Median nerve L.	33.4	30
Ulnar nerve L.	34.0	30
Peroneal nerve R.	58.2	54

Sensory Nerve Studies

Nerve	Onset Latency (ms)	Normal Onset Latency ≤ (ms)	Peak Latency (ms)	Normal Peak Latency ≤ (ms)	Amp (μV)	Normal Amp ≥ (μV)	Conduction Velocity (m/s)	Normal Conduction Velocity ≥ (m/s)
Median nerve R. (thumb)	2.6	2.6	3.1	3.1	21	20	50	50
Ulnar nerve R.	1.9	2.6	2.4	3.1	11	13	63	50
Median nerve L.	2.9	2.6	3.4	3.1	28	20	45	50
Ulnar nerve L.	2.1	2.6	2.6	3.1	11	13	57	50
Sural nerve R.	3.1	3.5	3.5	4.0	17	11	45	40
Superficial peroneal R.	3.7	3.5	4.2	4.0	11	8–10	41	40
Lateral ante. cut. R.	1.5	^b	2.0	2.3	11	11	^b	^b
Lateral ante. cut. L.	1.8	^b	2.3	2.3	4	10	^b	^b